FIG 6.

The cofactor of MtpC is 5-hydroxybenzimidazolyl cobamide. High-resolution matrix-assisted laser desorption ionization–mass spectrometry was used to characterize the corrinoid cofactor purified from the MtpC/MtpA complex. Several masses consistent with 5-hydroxybenzimidazolyl cobamide (shown in the inset) were identified. The predicted exact masses for C₆₀H₈₅CoN₁₃O₁₅P (m/z): 1,317.535 (100.0%), 1,318.539 (64.9%), 1,319.542 (20.7%), 1,318.532 (4.8%), 1,320.545 (3.5%), 1,319.539 (3.1%), 1,319.536 (2.9%), 1,320.543 (2.0%).